Direct reading loran navigation system



May 8, 1951 H. c. LAWRENCE, JR., ET A1. 2,551,681

DIRECT READING LoRAN NAVIGATION SYSTEM 5 sheets-sheet 1 Filed Feb. 26, 1949 May 8, 1951r H. c. LAWRENCE, JR., ET AL 2,551,68l

DIRECT READING LORAN NAVIGATION SYSTEM 5 Sheets-Sheet 2 Filed Feb. 26, 1949 EFEJ FOL/.UNER

May 8,.. 1951 H. c. LAWRENCE, JR., ET AL 2,551,681

DIRECT READING LORAN NAVIGATION SYSTEM Filed Feb. 26, 1949 5 Sheets-Sheet 3 ATTORNEY May 8, 1951 H. c. LAWRENCE, JR., ET A1. 2,551,681

DIRECT READING LoNAN NAVIGATION SYSTEM Filed Feb. 2e, Isa49 5 sheets-sheet 4 l Ma/#ff 4200A TSJ f www .im

ATTORNEY May 8, 1951 H. c. LAWRENCE, JR., ET AL 2,551,581

DIRECT READING LORAN NAVIGATION SYSTEM ATTORNEY Patented May 8, 1951 DIRECT READING LORAN NAVIGATION SYSTEM Howard C. Lawrence, Jr., Haddonfield, N. J., and Robert R. Freas, Jr., Jermyn, Pa., assignors to Radio Corporation of America, a corporation of Delaware 'Application February 26, 1949, Serial No. 78,482

' 13 Claims. (Cl. 343-103) 2,523,244, granted September 19, 1950, in the name of John D. Woodward. In the said Woodward system, a crystalv oscillator operating at one megacycle per second feeds into a chain of decade counters, the rstdecade counter being referred to as a one megacycle counter.

It has been lfound that in a systemoi the type described by Woodward, great care must be'taken in the design to make a one megacycle counter operate satisfactorily. Unless such care is taken,

diiculty will be encountered in the resetting operation of the counter. Also, unless such care is taken the coincidence tubes or circuits may not operate properly because of an insufficiently steep wave front on the pulses that the one megacycle counter output pulses must set on at 1 the coincidence circuits.

In the present system, just as in the Woodward system, it is desired to obtain pulse delays in one In the Woodward system this is accomplished by means of 1;

microsecond steps or intervals.

the one megacycle counter. According to the present invention, this is accomplished by means of a tapped delay line, for example, to lwhich 'delayed pulses (delayed to within nine microseconds or less short of the desired delay) are applied, the taps along the delay line being at one microsecond intervals. Thus, the one megacycle counter stage is eliminated along with all the diculties in making itoperate satisfactorily.

-The crystal oscillator is now operated at 100- kilocycles per second instead of being operated at one megacycle per second.

i Also, by employing the present invention, the system may be made more compact (l) because stray capacities in the wiring, etc. cause less trouble than when4 a one megacycle counter is employed, (2) because certain of the tubes may be made smaller since they do not have to supply power to lower impedance resistors to obtain fpulses of Very steep wave front, and (3) because Va smaller number of tubes is required.

Navigation systems of the loran type employ ``pairs of synchronized ground transmitting stavtions that emit radio pulses having a iixed time relation. Each pair of ground stations preferably transmits pulses at an assigned individual repetition rate for the purpose of station selection. The pulses are broadcast so that they may be received by means of equipment located in the aircrafts or ships whose positions are to be determined. By means of the receiving equipment, the operator on the craft determines the time difference between the pulses from the two transmitter stations of one pair as they arrive at the receiver. Since the radio pulses travel from the ground transmitters to the receiver at a known propagation rate (i. e., at the velocity of light), it is known that the position of the craft is at some point on a line corresponding to the time difference reading. By obtaining the time differencereading from a second pair of ground stations, a second line corresponding to the second time difference reading is obtained, and the intersect point of the two lines is the position of the craft. Special maps having theV time difference or loran lines printed thereon for the several pairs of ground stations are provided for use with the navigation system.

In order to measure the time difference in the arrival of successive pulses from a pair of ground stations, the receiving equipment is arranged to generate pulses at selected repetition rates. The `pulses may be kadjusted to have a definite time relation to time of arrival of the ground station pulses .and are provided for the purpose of driving or synchronizing cathode-ray deflecting circuits. VThe deilecting circuits produce cathoderay sweep traces on which the received ground -stationpulses are displayed. According to the present invention, these selected-repetition-rate and adjustably-delayed pulses are obtained from .a system that, as indicated heretofore, is an improvement on the system of counters and switching described and claimed in the above-mentioned Woodward application.

For the purpose of selecting a particular pair .of ground stations, the operator selects the particular pulse repetition rate for the driving or synchronizing pulses corresponding to the repetition period of the pulses transmitted from said pair whereby the deflecting circuits may be synchronized with the received pulses from the sethe receiver apparatus by setting the said counter switches to preselected positions. This preferably is done by turning a single station selection knob operating the several counter switches. Assuming the station selection switches are ganged, the station selection knob is turned to a position indicated on the receiver panel for obtaining sweep synchronizing pulses having the same repetition period as that of the pulses being trans mitted from the selected pair of ground stations. Now the received pulses from the selected pair f ground stations can be made to appear stationary on the cathode-ray sweep or trace Iwhereas those received from the other pairs 'of ground stations will move along the Vsame trace.

The pulses from the two transmitter stations of a selected pair will be referred to asA and B pulses, respectively, and the B pulse is identiiied in the present system as the pulse that occurs after or follows the mid-point of the other pulse period. In operation, the A and B .pulses are displayed, respectively, first on. two slowsweep cathode-ray traces and then on two fastsweep cathode-ray traces, thereby enabling the operator to 4obtain an alignment of the A and B pulses by adjusting another set of switches, referred to as delay-determining switches, so that the time difference between the pulses driving or synchronizing the cathode-ray deflecting circuits equals exactly the time difference between A and -B pulses.

In accordance with the present invention, certain of said delay-determining switches are switches connectedto said chain of counters just as described in said Woodward application, for example, but at least one of the delay-determining switches is connected to a tapped delay line or the like instead.

It will be noted that the chain of counters has two sets of switches connected to it, one for determining the repetition rate and the other for determining in part lthe amount a pulse is delayed. The action of each is independent of the action of the other.

The reason for employing a delay means with delay-determining switching connected thereto is that it simpliies the equipment and, what is more important, its use makes it possible to begin the counter chain with a lower frequency decade counter unit andthus avoid serious diiculties encountered in operating such a unit at a very high frequency.

The adjustment for the display and alignment of the A and B -pulses is accomplished by first setting the A lpulse at the left end rof the upper slow-sweep trace, when the receiving apparatus is switched to an operating position marked #1. The B pulse will then appear on the lower cathode-ray trace and a variable index marker ymay now be located under the B pulse, this being done by adjusting the several delay switches to delay the variable index marker the correct amount. The apparatus is then switched to a #2 fastsweep operation position so that the A and B pulses -appear on two fast-sweep traces, respectively. The starting time of the fast-sweep trace lon which the B pulse appears always coincides with the start of said variable index marker as determined by the delay switches, while the starting time of the fast-sweep trace on which the A pulse appears, coincides with the start `of the slow-sweep trace. Therefore, by a more exact adjustment of the delay switches, the adjustable fast-sweep wave is caused to start at the proper time to bring the A and B pulses into alignment. In order to insure exact alignment, the A and B pulses should be made to have the same amplitude, and an amplitude balance control circuit is provided for this purpose. After these adjustments have been made, the time diierence between the starts of the fastsweeps will exactly equal the time difference between the A and B pulses from the transmitters, and this time difference can be read directly from the settings of the delay switches.

The counter chain and switching system described in this application is not limited to use in-a navigation `sysinrl but, rather, is of general .application whereadjustably-delayed signals are desired and-especially, where it is also desired to select different repetition rates for the signals.

In .the specific .example herein described as applied to a navigation system, the counter chain comprises .three decade counters (rather than four as shown in the Woodward application) that divide by 10 followed by a frequency divider that divides by 4. The'rst stage of the divideby .4 unit is a binary -counter (a multivibrator) that is the last stage, strictly speaking, of the counter cha-in. The second multivibrator of the divide by 4" unit has no reset pulse'applied to it. The decade counters are preferably of the general type described in application Serial No. 580,446 filed March 1, 1945'in the name of Igor E. Grosdoff, now Patent No. 2,521,788 issued rSeptember 12, 1950. More specifically, lthe counter and counter switching combination utilizes principles described in application Serial No. 719,035 'filed December 28, `19.46 in the name of Charles J. Young now Patent No. 2,490,500 issued December 6, 1949, but, as yset forth in said Woodward application, includes improvements over and yadditions to the combination disclosed by Young.

Iii-accordance with the present example of the invention, the delayed pulses v`having a delay that is determined by the settings of the delay-determining switches are applied to a delay line and are taken off Ytaps `on the delay line-through a delay-determining switch for obtaining rdelays in steps of one microsecond.

An objeotof the present invention is to provide an improved method of and means for determining the time difference Ybetween electrical pulses.

A further object of the invention is to provide improved receiving equipment for a radio navigation system of the type utilizing the propagation of radio pulses from pairs of synchronized ground stations.

A still further-object of the invention is to provide an improved method .of and means for indieating the time'sdiierence between radio pulses transmitted from synchronized ground stations.

A y-still further-'object `of `the invention is to provide an improved method of and means for obtaining a direct reading of the time difference between radio pulses transmitted `from synchronized ground stations.

A still further object of the invention is to provide an improved means for obtaining vsignals that are delayed selected amounts.

A still further object of the invention Vis to provide an improved method of and means for obtaining signals of selected repetition rates that are delayed selected amounts.

A still further object of the invention is to provide an improved method of and means for producing pulses that recur at selected repetition rates and that may vbe adjusted in timing or phase.

Other objects, features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings in which: Y

Figure 1 is a block and circuit diagram of navigation receiving apparatus designed in accordance with one embodiment of the invention,

Figures 2 and 3, to be placed side by side, are block and circuit diagrams of the counter and the associated repetition rate switching and delay switching shown in block in Figure 1,

Figure 4 is a block diagram representing one pair of ground radio transmitter stations of the navigation system which transmit A and B pulses, respectively,

Figure 5 is a group of graphs which are referred t0 in explaining the operation of the navigation system shown in Figure 1,

Figure 6 is a group of graphs which are referred to in explaining the operation of the counter system shown in Figures 1, 2 and 3,

Figure 7 is a view of the slow-sweep cathoderay traces appearing on the screen end of the cathode-ray indicator tube that is included in the apparatus of Figure 1 and of the received pulses A and B as they appear on the traces when f they are aligned,

Figure 8 is a view of the fast-sweep cathode-ray traces on the cathode-ray tube indicator and of the received pulses A and B as they appear on the two fast-sweep traces, respectively, during the next step in obtaining more exact alignment of the A and B pulses,

Figure 9 is a view showing the fast-sweep traces of Figure 8 superimposed or collapsed for the nal alignment step and showing the A and B pulses exactly aligned and superimposed,

Figures 10 and 11 are circuit diagrams of the horizontal deilecting slow-sweep and fast-sweep circuits, respectively, employed in the system of Figure 1, and

Figure 12 is a circuit diagram of the delay line shown in block in Figure 3.

In the several figures, similar parts are indicated by similar reference characters.

THE COUNTER CHAIN AND ASSOCIATED RE- PETITION RATE' SWITCHES AND DELAY SWITCHES Referring to the navigation receiving apparatus shown in Figures 1, 2 and 3, the pulse-producing system comprises a crystal oscillator I0 that produces a sine wave voltage of stable frequency which in the example illustrated is 10-0 kilocycles per second, the repetition period being 10 microseconds. The frequency of the crystal oscillator output may be increased or decreased slightly by a manual adjustment as indicated at the control knob Il for obtaining a right or left drift of a received pulse on a cathode-ray sweep trace.

The crystal oscillator I0 drives a decade counter I3 to produce periodic pulses which recur at the rate of 10 kilocycles per second. The repeti- -tion period or time interval between successive pulses is, therefore, 100 microseconds.

The frequency of the 100 ,us pulses is divided by l0 by means of a second decade counter I4 to produce 1000 ,cs pulses. The frequency of the 1000 s pulses is divided by 10 by means of a third 'decade I6 to produce 10,000 s pulses, and the frequency of these is divided by 4 by means of As explained hereinafter, the

prise la'counter chain.V lThe output of divider I'I is in the form of a square wave having the repetition period of 40,000 es. V'This square wave is always symmetrical regardless of the repetition rate since the reset pulses are not applied to the second and last stage of the divider Il as will be understood from the later detailed description. The square output wave is passed through a cathode follower tube I8 and from it are obtained a vertical separation wave and, by means of a shaping circuit, a pulse for driving or synchronizing the iixed horizontal fast-sweep deflection as explained hereinafter.

A variable index marker pulse, which is obtained by way of a gate circuit No. 2, a delay line DI, and a switch ID, is adjustable in timing or delay whereby it may be shifted along the sweep trace when a slow-sweep is used and whereby it may be utilized to trigger the adjustable fastsweep when the fast-sweep is used.

The amount the variable index marker pulse is delayed is determined by the setting of time delay switches ID, SZD, S3131, StD, and SSD. With the exception of switch ID, these switches, as shown in Figure 3, are multi-pole, multi-contact switches that are connected to the several anodes of the multivibrator tubes in the counters. The switch ID is connected to taps on the delay line DL for obtaining a delay in one microsecond units as explained hereinafter.

The repetition rate of the pulse from gate No'. 2, as well as that of the other pulses taken off the counter chain, including the pulse taken off a gate circuit No. 1, may be varied for the purpose of station selection by means of repetition rate switches SER, SSR, SlR, and SBR which are similar to the delay switches SED, etc, and which are connected to the anodes of the counter tubes in a similar fashion. Pulses taken off the switches C SZR, etc. are passed through the gate circuit No. 1 and are supplied to a pulse generator i9 which niy comprise a Thyratron as explained hereina er.

The pulse output of gate No. 1 is also applied to each of the counters for resetting them as indicated in Figure 1 and as will be explained in the more detailed description with reference to Figures 2 and 3.

A detailed description of Figures 2 and 3 will be given later, but firstk the other parts of the navigation system will be explained. In the example being described, it will be assumed that the rst pair of ground stations transmit the A pulses with a repetition period of 40,000 s and transmit the B pulses with a like repetition period; that the second pair of ground stations transmit A and B pulses having a repetition period of 39,900 las; that the third pair transmits 39,800 as pulses; that the fourth pair transmits 39,700 s pulses, etc. It is apparent that for station selection at the receiving apparatus, the operator must be able to select corresponding repetition periods for the output pulses of the counter system which control the cathode-ray deflection cycle; namely, periods of 40,000 us; 39,900 ps; 39,800 as; 39,700 ps; 39,600 as; etc.

However, it may be preferred to employ a different group of repetition periods than the group of 40,000 as, 39,900 as, etc. assumed above. For example, repetition periods of 30,000 as, 29,900 as, etc. may be employed. Or, as another example, repetition periods of 50,000 es, 49,900 as, etc. may be employed.

meneer- 77 CATI-IODE RAY TRACE PRESENTATION,

At this point, it.may be Well to give a description ofthe operation of vthe receiving apparatus shown. in .Figure lV Withl particular4 reference to the'` cathode-'ray deecting Waves cathode-ray tube presentation:

In Figure 5,.the graphs X' andW show the switches |D, Sllyet'c.V (Fig-Lues 1 and 3)', as 'will' beexplained hereinafter, for aligning the A and B pulses. By means vofganged functionswitches, three switching positions identified as positions #1, #Zand #S are used successivelyin aligning the VA and B-pulses. It vWill be understood that While the pulses A and B and their corresponding fast-sweep traces appear alternately on the cathode-ray tubescreen, they appear to the eye to occur simultaneously because of persistence ofvision, lag olphosphorescence of the screen orboth.

As shown in Figure 5, the B pulse is` 'the `one that-occurs after the mid-point-or"` the A pulse period, and consequently the time interval., which elapses between the occurrence of a B pulse and the succeeding A vpulse Will be less than one-half pulse interval. As will be seenV in Figure 5, the startofV one fastestfeep. (lL- i) coincides with the start .of a slow trace, while the start' of the other fast-sweep (yf-g) coincides with the variable. index marker.

As already. explained, Ya momentary change of thexrecurrenceV rate will. change the location of thepulses on thetrace -by drifting them along the trace. Speoically, it is possible for the operator to locate the A pulse at the leit side of the upper slow trace, which in turn-will cause theB pulse 4to fall on the lower trace, andthe variable index marker may be made to coincide with the B pulse. Therefore, whenY the function switches are turned to position #2, the A pulse will occur during the trace described by the fixed f fast-sweep deflecting wave h-z, while the B pulse will occur during the trace described by the variable fast-sweep deflecting Wave -g.

A finer adjustment will permit'the operator to align the A and B pulses so that the time elapsed between the start of the respective rast-sweeps andv the corresponding pulses are equal and occurs during the expanded parts of the traces, thereby providing good accuracy for deteri ^ine ing the time delay.

In the present system, after the. A and B pulses have been aligned With the receiver svgtched successively to operating positions #1, #2 and #3, the desired time diference or time interval is read off the delayl switches iD, Sil), SSD, SAD, and S5D (Figures 1 and 3) which indicate, respectively, microseconds in units, tens, hundreds, thousands and multiples of ten thousand. The time interval thus obtained is the amount that the starting time t of the variable index marker has been delayed in time with respect to the mid-period d (Figure 5) of the deliecting Wave cycle in order to align the A and B pulses.

It may be-noted that the'upper fast trace hs-i (illustrated in Figure 8) is producedby the rst and the fast-,sweep .he-1i :ci the defiectingwave W. The

lower :fasttrace feg-(Figure 8) isproducedby the second fast-sweepwaye f-gof-.the ldeecting Wave W.

GENERAL DESCRPTIO'N OIF CATHODE 'RAY flLiiC'll` PRODUCNGV CLRCUITS f Referring to Figure` l and to the graphs: oi

Figure5the' output.- of thepulse generator I9k is supplied overV aconductor Gla to asloW-sweep. deflecting circuit H5 for producing asawtooth Voltage Wave X.

The output of, they divider ll is a, rectangular.`

voltage Wave which appears unchanged 4at the output of-` a' cathode-follower tube I8 as the Wave-C.,

To produce the fast-sweep wave h-i of der fleetingwave-W` (Figure 51)., thewave C'issuppliedover a conductor |93 to a dilierentiating circuit |05 to produce a pulse |05A. Thepulsek lilFiA4 is also utilized asthe .xedindex marker ofthe Wave V.

The circuit for. producing the variable index marker of wave V comprises-the counter chain, the delay line DLand the associated delay switching, the said markerbeing obtained from the adjustably delayed pulse U taken from the delay lineDL-by Way of the switch ID.' The delay line DL has delayed pulses supplied to itfrom the gate No. 2 as described hereinafter, the Vdelay line providing the final precise delay in steps of one microsecond units. It .is the Wave Uthat controls the` timingof the adjustable fast-sweep portion f-g of wave W.

The delayed pulse U is suppliedover a conductor ||9Avto the mixer |96. The mixed waves U and lApass through a clipper |2`| andappear as the Wave V. which drivesrthe fast-sweep deecting circuit |22 ,toy produce the Wave W;

When the system is in the No., 1 operating position, the xed and adjustable index marker pulses of the Wave'V are appliedto the vertical deecting plate 36B of the indicator' tube |39 through a lead 38.3, aswitch 35E; a resistor 384, and a lead 38|.

Description of mixer 106, etc.

Referring to Figures l and'll, the mixer circuit |06 and the clipping circuit` VH function to clip on" the negative pulses of the Wave |5A and to mix the remaining. clipped positive pulses with the pulses U.Y Thus, ,the wave V is obtained atthe outputof the clipper-mixer combination. The mixer IDR-which may consister two vacuum tubes having-acommon anode resistor as shown in Figure 11, reverses'the polarity of the pulses. The waves in the plate circuit of the mixer |06 are of equal` amplitude due to operation ofthe tubes in-.a condition Where gridand' plate voltage. approach equal amplitude. The width of 'theapplied VpulsesU and lAis `short compared to that ofthe plate pulses, the Width ofthe latter being controlled by a capacitor-resistor combination inthe plate circuitY and-therefore being independent of, the'width ofthe incoming Wave.v This capacitor-resistor combination comprises a capacitor Cl and the plate resistor RI.

The wave V is `supplied to the fast-sweep deliecting circuit |22 shown in detail in Figure 1l and described-hereinafter. The narrow negative pulses offwave V produce the fast-sweep Wave W'having the-useful .deflecting-,portions h-- and f--g.. The deflectingwaves W and X are applied vfrom the circuits |22 'and v| 5 through a Wave,- -selectingswitch |23 and through a `horiaontal deflecting amplifier' |24 to the horizontal deecting plates |38 of the cathode-ray indicator tube |39. As described in copending application Serial No. 589,320, now Patent No. 2,445,361, issued July 20, 1948, filed April 20, 1945 in the names of Garrard Mountjoy, George D. Hulst, Jr. and Earl Schoenfeld and entitled Radio Navigation System, the horizontal deflecting amplifier |24 may be provided with a switch (not shown) for changing the bias on the amplifier tubes when the function switch is changed from the slow-sweep position to the fast-sweep position and vice versa, thereby insuring optimum efficiency and undistorted gain from the amplifier tubes.

The switch |23, which is one of the function switches, has three contact points and three corresponding switch positions, referred to as operating positions, which are identified, reading clockwise, as positions #1, #2, and #3.

There are several other operation position or function switches, described hereinafter, that likewise have these three switch positions and which are ganged with the switch |23.

Switch |23, when in operation position #1, functions to apply the slow-sweep wave X to the horizontal deecting plates |38 and, when in operation positions #2 and #3, functions to apply the fast-sweep wave W to the deflecting plates |38.

The fast-sweep deflecting circuit 22 that is driven by the wave V (comprising the fixed and variable marker pulses) to produce the fastsweep wave W will not be described with reference to Figure 11.

The fast-sweep circuit Referring more specifically to the circuit |22 for producing the fast-sweep wave W, as shown in Figure 11, the circuit comprises a vacuum tube 3|6 and a pulse-shaping network that comprises two sections consisting of cathode resistors 33| and 332 shunted by capacitors 333 and 334, respectively, identied as network sections 3|1a and 3||b. The shaping network further comprises a delay line section 3|1c comprising series resistors 336 and shunt capacitors 331 connected across the cathode resistor 33| and terminated in a resistor 338 and in the cathode resistor 332. The fast-sweep wave W is taken off the resistor 338 through an adjustable tap 339, the setting of which determines the amplitude of the wave W.

In operation, the capacitors of the network sections 3|`|a and 3111 are charged through the anode resistor 34| and the tube 3|6 to a certain voltage level between successive pulses of the wave V to bring the tap 339 to the voltage e1 (Figure 5). Upon the occurrence of each negative pulse of the wave V, the tube 3|6 is driven to cut-off and the capacitors 333 and 334 discharge through the resistors 33| and 332, respectively. The section 3|'|ct comprising capacitor 333 and resistor 33| has a fast time constant whereby the discharge of capacitor 333 produces a voltage of steep slope across resistor 33|. The section 3|'i'a comprising capacitor 334 and resistor 332 has a slower time constant whereby the discharge of capacitol` 334 produces a voltage of less slope across resistor 332. These two voltages of different slopes appear at the tap 339 as the sum of the two voltages with the voltage of the steeper slope slightly delayed by the delay network section 3lc.

The wave form of the wave W following the said slight delay is approximately logarithmic,

It should be understood that the fast-sweep wave W need not be of the wave form described and, in fact, may be linear.

The above-described fast-sweep deflecting circuit is described and claimed in application Serial No. 583,255, now Patent No. 2,463,969, issued March 8, 1949, led March 17, 1945 in the name of George D. Hulst, Jr. and entitled Cathode Ray Deection Circuit.

As previously notedthe starting time t o f the fast-sweep wave f-g is determined by the adjustment of the pulse U (and in turn by the variable index marker of wave V) whereby the start of the wave ,f-g may be made to precede the received B pulse by the same amount that the start of the wave h-i precedes thereceived A pulse, this being the condition of alignment of the A and B pulses. It should also be noted that the wave f-g is identical with the wave h-z' whereby exact alignment of the A and B pulses on the cathode-ray traces is obtained (as shown in Figure 9) when the above-described timing relation exists.

An improved fast-sweep circuit described and claimed in copending application Serial No. 674,- 184, now Patent No. 2,449,169, issued September 14, 1948, filed June 4, 1946 in. the names of Paul F. J. Holst and Loren R. Kirkwood and entitled Deflecting Circuits, may be employed if desired.

The slow-sweep circuit Referring more specically to the slow-sweep deflecting circuit H5, as shown in Figure 10, it comprises a vacuum tube 3|8 and a network in the cathode circuit that comprises a cathode resistor 342 that has an adjustable tap 344 thereon and which is shunted by a capacitor 345. Positive bias is applied to the cathode of the tube 3|8 by connecting the lower end of cathode resistor 342 to the junction point of a pair of bleeder resistors 3|9 and 320. This prevents the tube 3|8 from drawing current at the end of the sawtooth cycle so that flattening of the sawtooth wave is avoided. The operation is as follows: Each time one of the positive 20,000 ,as pulses from the lead 6|a is supplied to the'grid ofthe tube 3|3 by Way of a coupling capacitor 32|, 'the capacitor 345 is charged suddenly from the anode Voltage supply through the tube 3|8 to a certain voltage level to bring the tap 344 to the voltage level e2 (Figure 5). At the end of each positive pulse, the capacitor 345 discharges slowly through the resistors 342 and 3|9 thus producing successively the slow-sweep sawtooth wave portion a-b and the sawtooth wave portion c--oZ at the tap 344. i

In Figures 10 and 11, the values of certain circuit elements have been indicated, merely by way of example, in ohms, megohm-s, microfarads and micro-micrcfarads.

THE RADIO RECEIVER The A and B pulses from a pair of ground stations (Figure 4) are received by a radio receiver of the superheterodyne type comprising a radio frequency amplifier indicated at 36|, a converter 332, an I.-F. amplifier 3.63 and av second detector and video frequency amplifier 364. The A and B pulses are supplied with positive polarity over a conductor 366, a conductor 33| and a capacitor 382 to the upper vertical deecting plate 333. Thus, the A and B pulses may be made to appear, as shown in Figures 7, 8 and 9, on the horizontal cathode-ray traces. The A and B pulses are made to appear with equal nfacilitating the ,A and B'pulse alignment.

.amplitudeon the cathode-,ray tube screen by employing a differential gain control circuit described hereinafter.

"'SLOW-SWEEP AND FAST-SWEEP TRACE YSEPARAUI-"ION The slow-sweep traces a-b and c-d ,are separated as illustrated in .Figure '7 while the re- .ceiver is on the #l `operation position by means .of the rectangular wave C (Figure supplied lornfthe cathode follower tube I8 (Figure 1) over `aconductor 369 to .the #l contact point o Va trace separation switch 31|, and over a conductor 1312 .to -the upper delecting `plate 368 of the cathode- .ray -tube |39. Thus. the portion of the wave-C, Whichis positive as it appears on .the upper plate .368,holdsthe cathode-rayvdeflection up a certain amount duri-ng 'the-occurrence of theslow-sweep -deflecting wave c--d.

`The fast-sweep traces f--g andh-i areseparated.l as illustrated irrFigure 8 during the #2 operation position also by means ofthe rectangular ewaveC.

FAST-SWEEP' BLANKING Blanking is provided so that only the traces f--g and h-iappear onthe cathode-.ray screen whenin'the #2 Yand #3.fast-.svveep operatingpostions. 'This blanking is provided by meansv of the negativefportions of the .wave Y as it'appears on the anode of the tube 3H:` `(Figure 11) of the TRACE BRILLIANCE CONTROL The.diode 32|| isprovided to control the brilliance ofthe traces on the.cathoderaytube screen "by preventing changesin bias on the'cathode-ray tube grid321 due tothe rapplication of blanking pulses. A leak resistor 328 is connected across "the diode 321|` and thecathode of the diode 324 is .connected to. a variable bias voltage source (not shown) `In operation, during'the periods that the blankling-waves are positive at the anode of the ldiode 5324,"the impedance of the diode 324 `is very-V low so that itsanode is Ypractically at the bia-s potentiallof its cathode. Thus, regardless of the'form :of the blanking wave and regardless of whether any blanking wave is being applied, `the voltage aonfthe grid i32'| of the cathode-ray tube 'during the cathode-ray sweeps is substantially .the voltage .on-.thecathocle ofthe diode 324.

DIFFERENTIAL GAIN CONTROL V(LIRCUI'I A differential gain control circuit for the R.-F. amplifier 36| of the radio receiver preferably is provided, as shown in Figure 1, for the purpose' vofz'keeping the amplitudes of the VA zand B Vpulses 4substantially alike at the .receiver output, thus The gain control circuit includes a resistor '343 connected between the anodes of the 'two tubes of the last multivibrator in the -nal divider |'I (Figures 1 and 2). An Vadjustable differential gain balance tap onl resistor 343 Amay be moved toeither side of the center thereof to decrease the gain of the :EL-F. amplier36 I during :either the reception through the switch 348 anda ,conductor 349 `tothe gain control grid of an amplier tube in the R.F..amplier 36|.

The ,differential gain control .operation with the receiver oli-,either #2 or #3 .operation position is asfollows:

.When ,the gain .balance tap is at the centerjof resistor 343, no voltage `wave is applied to 'the `diode 341. When .thetap ison oneV side of this center or balance position, a waveof one-polarity visapplied- .to the diodeY 34.1; when the tap `isvon .the other-.side of .the ,balance point, a waveof the Y opposite polarity is applied to .the diode 341. The

V0f the pulse A or .the pulse B. Thevoltage Vat the gain balance tap is'supplied through a lead 340, a capacitor @4l-and aresistor 336 tothe anode of a diode 341 and to the #2 and #3 contact; points of .diode 3M functions to supply a negative -biasduring the .negative .half-cycle following a positive .cycle of, an applied wave. VFor example, a positive .halfcycle causes diode current to charge capacitor 344., .and during the following negative halfcycle thecapacitor 344 dischargesslowly through .a resistor 35| connected across thegdiode 341 thus .making the anode of diode 341 negative with respect to ground and reducing the gain of the R.-F. aniplifler 36| whilethe B pulse (or the A pulse.) lis'beingamplified. y

'With switch 348 on the #l operation position Yfor ,pulse alignment, normal operating bias voltage -V'is on the R.-"F. amplier 36 DETAILED DESCRIPTION OF COUNTER CHAIN AND SWITCHING OF FIGURES 2 AND 3 A more detailed description Vwill now be given describing the system of counters, switches and gatesiforobtaining pulses of the desired repetition Yrate, and of the desired delay. The specic'systernshown injFigures 2 and provides eightdifferent repetition rates of' 40,000 as; 39,900 es;

39,800 ps. etc. for selecting any one of eight pairs 'tioned Woodward application, consists of multivibrator-like locking stages y,comprising double triodes Vl, V,2, V3 and Vil. "These stages each vhave two positions of rest at. one or the other of which they stay locked, when ,tripped thereto, until some applied voltage or current trips them again to lock them in the other position. In the embodiment shown, application of negative voltage tothe anodes andthence to the grids of the locking circuit tubes will reduce current in that tube drawing current and start the tripping `action which switches thecurrent through the other tube. Decade counters No. 3 and'No. 4 are similar and to simplify the diagram have been i1- lustrated by rectangles. VThe frequency divider or counter No.6 is illustrated in detail and comprises only two multivibrators Ml and M2 since it divides by 4. The rmultivibrators in this counter are similar to those employed in thedecade counters. -Howeven the rststageMl is the final stage `of the counter chain. .The second` stage 15 M2 has no reset pulse applied to it and Yit does assisl 13 not supply any pulse to the coincidence tube of the repetition rate system as will be apparent from the following description.

The repetition Tate switching Associated with each decade counter is a threepole, ten-position switch (Figure 3) for determining the pulse repetition rate. These switches are referred to as SZR, SBR, and SllR. While ten switch positions are shown for clearness of explanation, not all of them are useful in selecting the eight stations in the example described. There is also a single-pole two-point switch SSR for the binary counter Ml.

The switches SZR, SER, S4R, and S5R and the contacts thereof are coupled to the anodes of the locking circuit tubes whereat the potentials rise and fall depending on which tube of the pair is drawing current. For example, the

anode ViA of the left-hand or A section of the tube VI is connected to alternate contacts of pole Pl of the three-pole switch SER. The anode VIB of the right-hand or B section of tube V l is connected to the remaining contacts of this pole. The anodes V2A, V2B, and VSB of tubes V2 and V3 are connected to staggered pairs of contacts of the second pole P2, etc. The basic details of each decade and how it operates is covered fully in Grosdoff application Serial No. 580,445, referred to above and consequently, no detailed explanation will be given here. Associated with the binary Mi of counter No. 5 is the single-pole twoposition switch S5R that functions with switches S2R, S3R, etc. for determining the repetition rate. Although not so illustrated, the switches SZR, SSR, etc. preferably are ganged so as to be operated by a single station selection knob.

The basic purpose of the counter circuit is to produce output pulses after the counters have counted a predetermined number of master oscillator cycles or pulses. The start of the counting is controlled by a gate circuit No. l (Figurek 1) and comprising tubes 2, 28, 2S, 30, and 34 (Figure 3) as will be explained later. The development of the counter chain output pulses that are to be produced after the predetermined count has been reached is obtained by combining the proper voltages from the anodes of certain tubes in all four counters. For example, to select station LI the repetition period of the last multivibrator M2 of counter No. 5 is made 39,900 microseconds.Y Since the first stage Mi of counter No. 5 is thel final one in the counter chain to be reset, as explained hereinafter, the desired result is obtained by making the repetition period of its output wave D (Figure 5) one half the said period of 39,900 ,is or 19,950 as. Therefore the switch S2R on counter No. 2 is set on position 5 which is the tens count, switch SSR on counter No. 3 is set on position 9 which is the hundreds count, switch S4R on counter No. 4 is set on position 9 which is the thousands count, and switch SBR on counter No. 5 is seton position l whichV is the ten thousands count.

The voltage pulses collected by the switches are combined by means of ve vacuum triodes 2, 23, 29, and 30. rlhe tubes are in conven tional circuits including grid leak resistances BR connecting the switches to ground. Each triode is biased by means of a voltage drop across a 'oy-passed cathode resistor. This combination of pulses is obtained by the connections of said switches to the control grids of these four tubes. The anodes of the tubes are connected together to produce a single pulse, which represents the 14 sum of the collected pulses, and feeds the same byjway of resistors 31, 38, 39 and 4| and common .resistor 42a to the grid 33 of a final combining or coincidence tube 34. The tube 34 is connected in an amplier stage with its grid grounded by a resistor 45 and its cathode grounded by a resistor 45 and its anode connected to the plus terminal of a direct current source. The anode of amplifier tube 34 is coupled by a capacitor 4l to the control grid 48 of an output or reset pulse generator tube 43, the purpose of which is to deliver the combined or output pulse to all of the tubes in all of the decade counters and to the tubesin the binary counter Ml to trip the same back to their starting position for successiveoperation of the counter chain and also to deliver a pulse of the desired repetition rate to the slow sweep generator by way of the lead tia. A negative bias voltage is applied to the grid 48 of tube 40 through a resistor 45a.

Referring to decade counter No. 2 which has its switch SER set at position 5, it is noted that for each position of the switch, a ldifferent cornbination of voltages from the eight tubes of the counter are used as explained in the Grosdoil.` application Serial No. 580,446. The voltage on the switch SER as applied to the grid of tube 2 reaches a certain maximum positive valuey only when the count is at the value for which the switch position is set and the nal desired output pulse applied to the grid of tube 34 is obtained only when the proper combination of voltof tubes V IB and V3B and V4A. This combination of three voltages raises the control grid of tube 2l' above its cut-off point so that conduction is initiated in tube 21 and the potential on its anode and at resistor 31 falls. The procedure for selecting voltages by the switches will be understood by referring to the graphs of Figure 6.

The several graphs of Figure 6 show the voltages appearing at the several anodes of the tubes Vi, V2, etc. The graph identified as VIA shows the voltage on the anode of the left-hand or A section of tube VIA, for example. The dissymmetrical characteristic of the graphs for the tubes V2 and V3 results from the feedback employed to obtain a decade count as explained in Grosdoi application Serial No. 580,446, The dots indicate the plates that are selected to obtain a given count. For example, the anodes VIA, V2A, and V4A are connected to switch points 0 to obtain the count 0 when the switch is set on said points 0. A similar action takes place in tubes 20, 23 and 30 when the proper voltages are obtained by the settings on switches S3R, S4R, and SBR. When the final pulse which represents the final combination of voltages from the tubes 21, 2B, 29, and 30 is reached, the

tube34 is never sufciently negative to cut this tube off until the time occurs when tubes 2'l,

- 28, 29 and 30 are simultaneously conductive,` this Ipoint being `when the. counter. chain has reached the predetermined. .count for whichit. is adjusted.

At'the. instant when the counter chain produces its output pulse at the plate of` tube 34,

Vspectively, of the repetition rate switching cirthis output pulse is applied to theA pulse gen- 5 SllD, and SED determine the delay in hundreds, erator tube 49 which. preferably is a vapor tube thousands,y and tens of thousands, respectively. such as a Thyratron. so that .a largecuri'ent out- For example, if .the delay switches SZD, SBD, put isy obtained. at. the. output terminal 5l of the SAID, andy SED are on positions 5, 7, 6, and 0, reload resistor 46a. Preferably, the tube 49 disspectively, as illustrated, when pulse alignment charges a` capacitor 49a which receives a charge 10 on the cathode-ray tube screen is obtained, then from theA B-lsourcethrough a resistor 49h. the reading from these switches is 6750 micro- Thus a high energy output pulse is produced. seconds, there being no microsecond unit read- -From terminal 5I Vthe pulse is applied by way ing so that the last figure is zero. For convenof". condenser 52 and. lead .42. to reset the counters ience in setting the delay switches SED,v SSD,

i of the counter cha-in back to the zero .orY start- 15 etc., their ganged switch arms preferably .are ing position. This resetting function. is accornoperated by rotatable knobs 2D, 5D, etc. which plishedby application of the output pulse, which carry pointers that indicate the delay setting. is positive in polarity, to the. grid circuits of all Todetermine the delay in one niicrosecond the tubes in the counters ywhich draw current units the. pulses from the tube 62 (delayedto inthe starting position. As previously stated, 20. Within. nine microseconds or less short of the the reset pulse isnot appliedto the multivibrator desired delay) are applied by way of lead H9 to M2 of the frequency divider Il. the delay line DL which provides a delay of one The reason for not applying .a reset pulse to microsecond per section. The line. DL may be of the multivibrator M2 is that it must supplya the conventional 1r section type suitably termix symmetrical square wave (wave C in Figure 5) 25 nated in aresistor TR to make it non-reflecting. i.ust as in the case of the Eccles-Jordanv oscil- Taps are taken off theinput end of the line DL later shown in Minneman application Serial No. and off the end of each section and connected to 744,239, now Patent 2,515,464 issued July 18, the switch. contact points of the switch ID. The 1950. Furthermore, there is no necessity for contact points are numbered 0 to 9 to indicate applying a reset-pulse tothis last multivibrator 30 microsecond units. The iinal delayed pulse is for changing the repetition period. This will be taken off the switch. arm of switch lD'by the understood from the following, lead HSA.

If the desired repetition period of the wave It will be apparent that with the switches ID C (Figure 5) from the last multivibrator M2 is to 5D on positions .8, 5, 7, 6, and 0 as illustrated, to be 39,900 as, it is only necessary to make the 35 the pulse appearing on lead I ISA is delayed 6758 repetition period of the-wave D (Figure 5) from microseconds, theunit reading being obtained by the preceding multivibrator MI 19,950 ,is since means of delay line DL.

" the last multi-vibrator divides by 2. This, of This reading of `6758 microseconds locates one course, is accomplished by the resetting action of thenavigation or loran lines of position on described. Similarly, for any other repetition 40 the map prepared for use with the equipment. period, the switches SZR, S3R, etc. are vset to Instead of tapping a delay line or ne work, a

. give the desired repetition period for the output pick-up electrode may be associated with the dewaveD of the first multivibrator MI of counter lay l-ine so that it has capacity to diiferent points No. 5, which repetition period is one-half .that in the networkasthe electrode is moved. of Ythe output wave C. 'For the particular exam- 45 The present invention is not limited to the use ple assumed; the different switch settings for of a particular kind of delay network or delay selectingV eight different pairs of' stations L0, Ll, means or to any particular way of taking the de L2 etc. may be charted as follows: layed pulses oli the delay network.

Repetition. rate switching STATION L0 L1 L2 L3 L4 L5 Le L7 Rem 20,000 19,950 19,900 19,850 19,800 19,750 19,700 19,050Y

vS211 0 5 0 5 0 5 0 5 saR 0 0 9 s s Y 7 7 0 S411 0 9 9 9 9 9 9 9 S511 2 1 1 1 1 1 1 1 The delay switching While the use of an electrical delay line is pre- .ferred because of its reliability and simplicity,

Th? @may swtche? SED' S3331 SAD and 55D other suitable delay means are well kncwnin the are 'similarto theuswitche's illustrated for deter-V mi There may be mentioned by Way of exam? mining the repetitlon period and they are con- 05 ple, delay multivibrators and phantastron delay nected to the chain of counters 1n the same way. means.

The Yoltages taken Off the delay Switches 'fue It should be understood that the steps of delay supplied to vacuum tubes 5l, 58, 59, and 69 which in the delay means *are not limited to one mc10 comprise'the gate circuit N012 (E igure 1). These Second steps no1. is the total delay provided by tubes and than assoclad Clcuts CrreSpolld t0 70 the delay means limited to nine microseconds. the tubes 2l, 28, 29, and 3|! and their associated AS an example of another Suitable design the circuits previously described. delayrline DL might have 19 Sections of one The coincidence tube El (to which the outputs miorosecond delay each to provide delay steps of of tubes 5'! .to 66 are applied) and the VThyratron v one microsecond. In this example the oscillator tube V$2 correspond tothe vtubes Bilanci. 69, re- 75 I0 would operate at 50 kilocycles per second and the counter i3v would divide by 5.V Thedelay switch 2D would then give delay in steps of 20 microseconds.v To obtain the proper repetition rates with this arrangement a delay line to give a delay of 10 microseconds may be put in the output circuit of the gate circuit No. 1 and provided with switching so that the 10 microsecond delay is switched in whenever the switch S21?, is switched to 5, i. e. to its position for stations L1, L2, etc.

It will be noted that since the last counter stage supplying pulses to the gate tube e@ is the binary Mi, the coincidence tube El would supply output pulses of a repetition period of 29,000 s or less, depending on the selected repetition period, in the absence of some further circuit action. Double this repettion'pericd is desired, of course, for driving the fast-sweep circuit-to obtain the adjustable fast trace f-g (Figure 5). The desired repetition period is obtainedby, in effect, blanking out alternate pulses as indicated in Figure 5 so that only the 40,0% fis repetition period pulse U appears on the lead H9 and,

therefore, on the lead HSA.

This blanking effect is obtained by applying to the grid of gate tube by way of a lead l@ a square wave from the last multivibrator M2. This wave is the same as wave C (Figure except that it is of the opposite polarity, being taken olf the opposite side of M2 from the side supplying the wave C. Thus, the grid of tube Sii is held negative during the master period (see Figure 5) whereby the pulse from the binary MI cannot pass through tube Sil during said period.

The amount a pulse is delay is not aifected by changes in the pulse repetition rate because the Aamount of delay is less than the shortest repetifect the repetition rate since they do not aifect the resetting circuit.

It will be apparent that the system of counters, switches, gate tubes, coincidence tubes and delay line described herein for obtaining pulses of selected repetition rates and selected delays is of general application and is not limited to its use in navigation apparatus. plication it probably would be desired to omit the lead l@ so that there would be no blanking action. In that case the output pulse on lead l i9A would have a repetition period of 26,000 [is or less as desired andthe amount oi the delay would 'be measured from the time of occurrence of any reset pulse, not just from the reset pulse occurring at the midpoint d as in the navigation system application.

From the foregoing description, it will be un'- derstood that we have provided an improved navigation apparatus of great accuracy that determines time intervals or differences that are easily read by an operator; that we have also provided va system of counters and switching of general application which supplies pulses that may be adjusted to any one or a wide range of -repetition periods, with the pulses of a selected repetition period delayed with great precision For general ap- 18 and that we have provided a system that produces pulses delayed in one microsecond steps or intervals while avoiding the difiiculties encountered in operating a one megacycle counter in combination with coincident circuits.

PROCEDURE IN' lVAKIlGrv A TKME MEASUREBEELNT rThe successive steps in making a measurement of the time interval between `the A and B pulses from a pair of ground stations will now be described.

Ai-ig'nmcnt of A and B pulses Position #if-After a particular pair of ground stations has been selected with the receiver set on the #l operation position of the function switches, the A and B pulses will appear stationary on the two traces a-b and c-d. A suitable drift switch such as knob H of oscillator I0 is operated to drift one of the pulses onto the upper trace c-d and over the fixed index marker at the left end of this trace. The other pulse will now appear on the lower trace a-b. The pulse on the trace c-d is the A pulse and the pulsefon the trace a-b is the B pulse. That this is true will be evident by referring to the graphs of Figure 5.

Next, the starting time t of the variable index marker of wave V is adjusted by setting the delay switch knobs 5D, 2D, etc. to bring the variable index marker under the B pulse. The variable index marker is now carefully adjusted so that its position with respect to the B pulse is substantially the same as the position of the xed index marker with respect to the A pulse.

Position #2.-Next, referring to Figure 8, the receiver is switched by the :function switches to the fast-sweep operation position #2 which results in the A and B pulses appearing on the traces h--z and f-g, respectively. As shown in Figure 5, the start of the variable index marker pulse of wave V determines the start of the second fastsweep portion f-g of wave W, the two starting practically simultaneously. By operating suitable drift switches such as the knob ll of the crystal oscillator l), the A and B pulses are drifted to the left ends of the traces where they are on the more expanded portion of the fast-sweeps. They are then closely aligned as shown in Figure 8 by operating one or more of the delay switch knobs ID, 2D, etc.

Position #3.-The final alignment of the A and B pulses is done on operation position #3 with the two traces f-g'and h-z' superimposed as shown in Figure 9. The front edges oi the A and B pulses are now exactly aligned, usually by operating only the switch knob ID. The time reading can now be made from the settings of the delay switch knobs as shown by the positions of the pointers on the knobs ID, 2D, 3D, 4D, and 5D.

For example, ir the pointers of the switch knobs iD, 2D, 3D, QD, and 5D read 8, 5, 7, 6, and 0, respectively, the reading is 6753 microseconds.

We claim as our invention:

l. Apparatus for determining the time interval between two time-spaced pulses, said apparatus including a pulse coincidence indicator for indicating visual coincidence of said two timespaced pulses applied thereto, a chain of counters for producing an adjustably-delayed pulse, means comprising count-selecting means connected to said chain of counters for determining the amountof delay of said delayed pulse, a delay means, means for applyinggsaid delayed` pulse to said delay means, means for obtainingvfrom said delay means a pulse that is further delayed a selected amount by said delay means, means for applying said further delayed pulse to said coincidence indicator for bringing said two timespaced pulses into visual coincidence, and means for indicating said time interval as a function or thev adjustments of said count-selecting means and said delay means.

2. Apparatus for'determining the time interval between two time-spaced pulses, said apparatus including a pulse coincidence indicator for indicating coincidence ofsaid two time-spaced pulses, a chain of counters for producing an adjustably-delayed pulse, means comprising countselecting means connected to said chain of counters for determining the amount of .delay of said delayed pulse, a delay line, means for applying said delayed pulse to said delay line, delay line switching means for taking said. delayed pulse o selected points along said delay line toV obtain a pulse that is further delayed a selected amount by said delay line, means for applying said further delayed pulse to said coincidence indicator for bringing said two time-spaced pulses into coincidence, and means for indicating said time interval as a function of the adjustments of said count-selecting means and said delay line switching means.

3. In a navigation system receiver for receiving two time-spaced pulses that are transmitted in a predetermined time relation from two geographically-spaced stations, respectively, said receiver including a pulse coincidence indicator for indicating coincidence'oi said two time-spaced pulses, a chain of counters for producing an ad.- justably-delayed pulse, means comprising countselecting means connected to said chain of counters for determining the amount of delay of said delayed pulse, a delay means, means for applying said delayed pulse to said delay means, means for obtaining from said delay means a pulse that is further delayed a selected amount by said delay means, means for applying said further delayed pulse to said coincidence indicator for bringing said two time-spaced pulses into coincidence, and `means for indicating a navigation line of position as av function of the adjustments of said count-selecting means and there is means for supplying to the input endV of said chain of counters a signal having a certain repetition period, and wherein said delaydmeans provides increments of delay that are smaller than said certain repetition period.

5. In a navigation system receiver-for receiving two time-spaced pulses that are transmitted in a predetermined time relationlirom two geographically-spaced stations, respectively, said receiver including a pulse coincidence indicator. for indicating coincidence of said two time-spaced pulses, a chain of counters for producing an adjustably-delayed pulse, means comprising countselecting means connected to said chain of counters for determining the amount of delay of said delayed pulse, a delay line, means for applying said delayed pulse to said delay line, delay line switching means for taking said delayed pulse off selected points along Said delay Vline tovobtain a pulse that is further delayed a selectedamount., by said delay line, means for applying said fur- 2 0 therjdelayed. pulse toV said coincidenceindicator for bringing said twotime-spaced pulses int coincidence, and means1 for indicating 'a navigation. line of positionV asy a function .ofthe adjustments of said count-selectingmeans andisaid'delay line switching means when, coincidence. of said time-spaced pulse is obtained at said' indicator. i

6. In combination, a chain of counters, means comprising count-selecting means connectedto each of said counters for obtaining output pulses and for determining the repetition rate of` said output pulses, saidfrepetition rate. determining means also includingmeans for. resetting said counters by said output pulses and-atV the same time restartingl the cycle of,V operation of the counter chain, additional means-comprising additional count-selecting means connected to each of said counters forobtainingother output lpulses of said repetition rate andV for determiningthe delay of rsaid otherA output pulsesw-ith respect to the startof said cycle, a delay means, means for applying said other output pulses toisaid. delay means, meansv for obtainingfrom said delay means pulses that are further delayed. al selected amount by saiddelay means,`

7. The invention accordingftoclaim wherein there is means for supplying to the input end of said chain of counters a sig-nal.. having a certain repetition period, and wherein said delay means provides increments ofA delaythat .are smaller than said certain repetition period.

8. In combination, a chain ofk counters, means comprising count-selecting. means connected.` to each ofA said countersior obtainingoutputpulses and for determining therepetition rateof said outputY pulses, said repetition rate determining means also including means. .for resetting said counters by said output pulses and. at thesame time restarting the cycle of. operation of` the counter chain, additional*meansV comprising addi,- tional count-selectingv means connected to each of said counters for obtaining other output pulses of saidv repetition rate and for determining the delay of said other outputV pulses. withrespect to the start-of. said cycle, atapped delay. line, means forapplying said. other output pulses to said delay line, delay line switching meansrffor taking saidother output pulses ce1-V selectedtapped points along said delay line tov obtain pulses that are further delayedv a selected-'amount by saidldelay line.

9. kIn combinationa chain of counters, a stable oscillator connectedto supply signalcontinuously to the/,high` frequency end of said chain of counters, means. comprisingy count-selecting means connected to each ofsaidcounters for obtaining output pulses and forl determining the repetition rate of said output pulses, said-repetition rate determining` means also including meansfor resetting said counters by said output pulses andat the same time restarting the cycle of operation of the counter chain, and additional means comprising. additional count-selecting means connected to each of said counters for obtaining other output pulses of said repetition rate and for determining theY delay of said other output pulses with respect to the start of said cycle, a delay means, means` for applying said other output pulses to said delay means, means for obtaining from said. delay means pulses that are further delayed a selected amount by said delay means.

10.v The invention according to `claim 9wherein said delay means provides increments of delay 2l that are smaller than the repetition period of the signal supplied by said oscillator.

11. In combination, a chain of counters, a stable oscillator connected to supply signal continuously to the high frequency end of said chain of counters, means comprising count-selecting means connected to each of said counters for obtaining output pulses and for determining the repetition rate of said c-utput pulses, said repetition rate determining means also including means for resetting said co-unters by said output pulses and at the same time restarting the cycle of operation of the counter chain, and additional means comprising additional count-selecting means connected to each o said counters for obtaining other output pulses of said repetition rate and for determining the delay of said other output pulses with respect to the start of said cycle, a tapped delay line, means for applying said other output pulses to said delay line, delay line switching means for taking said other output pulses off selected tapped points along said delay line to obtain pulses that are further delayed a selected amount by said delay line.

12. In combination, a stable oscillator operating at 100 kilocycles per second for supplying signal at a comparatively high frequency, a chain of counters, means for supplying said signal to the high frequency end of said chain of counters,

each counter having a count-selecting means, a

coincidence tube or circuit, said selected counts from the counters of said chain being applied to said coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter occurring simultaneously, means for resetting said counters by said output pulse and at the same time restarting the cycle ofoperation of the counter chain whereby the repetition rateofsaid output pulse is determined by the count selection at each of the counters; each counter of said chain having an additional count-selecting means, a second coincidence tube or circuit, the counts selected by said additional countselecting means being applied to said second coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter applied thereto occurring simultaneously and whereby said second output pulse has a delay determined by the count selection of said additional count-selecting means and a repetition rate determined by the count selection of said first count-selecting means, a delay means, means for applying said other output pulses to said delay means, means for obtaining from said delay means pulses that are further delayed a selected amount by said delay means.

13. In combination, a stable oscillator operating at 100 kilocycles per second for supplying signal at a comparatively high frequency, a chain of counters, means for supplying said signal to the high frequency end of said chain of counters, each counter having a count-selecting means, a coincidence tube or circuit, said selected counts from the counters of said chain beingr applied to said coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter occurring simultaneously, means for resetting said counters by said output pulse and at the same time restarting the cycle of operation of the counter chain whereby the repetition rate of said output pulse is determined by the count selection'at each of the count-ers; each counter of said chain having an additional count-selecting means, a second coincidence tube or circuit, the counts selected by said additional count-selecting means being applied to said second coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter applied thereto occurring simultaneously and whereby said second output pulse has a delay determined by the count selection of said additional count-selecting means and a repetition rate determined by the count selection of said rst count-selecting means, a delay line that is tapped to provide delays in increments of one microsecond, means for applying said other output pulses to said delay line, delay line switching means for taking said other output pulses ofi selected tapped points along said delay line to obtain pulses that are further delayed a selected No references cited, 

